The invention relates to a reversible compressed air motor for compressed air tools, in particular for compressed air wrenches.
A compressed air wrench of this type is known from German OS No. 21 24 149. Axial channels for the supply of air are provided in a rotor cover which closes off the cylinder formed in the casing, in which cover one end of the rotor is mounted. The channels open into the compressed air inlet provided in the cylinder, which supplies compressed air radially to an expansion chamber.
During the rotation of the rotor, after travelling past the compressed air inlet, the expansion chamber is connected to a radial air outlet which consists of bores in the cylinder arranged one behind the other in the axial direction in the plane of the major semi-axis, which bores discharge the compressed air radially. The compressed air escaping radially interferes considerably with the operation of the compressed air wrench, so that basically deflection pockets for the compressed air are provided, which necessitates additional construction expenditure.
Furthermore it has been found that on account of the radial outlet openings lying diametrically with respect to each other, and the intermittent escape of waste air, the cylinder wall is subjected intermittently to pressure surges, which leads to vibrations and pressure surge agitation of the entire compressed air wrench. These vibrations lead to considerable air noise of a high sound level. Therefore, as a rule, additional structural means must be provided in order to reduce the nuisance as regards noise and vibration to a tolerable limit.
The known compressed air motor is a twin-chamber motor and in all has four radial compressed air inlets separated from each other, which each lie in one quadrant of the elliptical cross section. Two diametrically opposed inlets respectively are provided for clockwise or anti-clockwise rotation of the motor, in which case the inlets are located close to the minor semiaxis. The radial outlet openings are provided in the plane of the major semi-axis, the overall construction being symmetrical both with respect to the minor as well as to the major semi-axis. This symmetrical arrangement produces a relatively small expansion space for the compressed air introduced, in which it must exert accelaration forces on the rotor. Since the opening of the outlet openings already begins when the leading vane in the direction of travel is located at the apex of the inner contour, the expansion work of this construction is relatively low. Since moreover it must be ensured that the compressed air inlet and air outlet cannot be connected directly to each other, a certain spacing of the vanes or minimum number of vanes is absolutely necessary. However, a high number of vanes implies a high air consumption.
For reversing the motor from one direction of rotation to the other, a separate reversing valve is provided, which guides the compressed air supplied either through one pair of diametrically opposed inlets for clockwise rotation or through the other pair of opposed inlets for anti-clockwise rotation. On account of the symmetrical arrangement, the torque of the motor in both directions is identical, but relatively low on account of the small expansion chamber.